The invention relates generally to power management in electronic circuits and more particularly, to power management based on a direct measure of a circuit's power consumption.
Power management techniques in, for example, a computer system typically employ thermal sensors and/or inactivity timers. Thermal sensors provide an indirect mechanism to monitor and control a circuit's power consumption by measuring the heat generated by one or more components within the circuit. System response to an over temperature condition is generally to reduce the operating speed of the computer system's central processing unit (CPU). This may be accomplished by asserting a stop clock signal (an input signal to many modern CPU devices) for some period of time, typically in a pulse width modulation (PWM) fashion, or by actually reducing the system clock frequency.
Many modern computer systems use only a limited number of thermal sensors. Most personal computer systems use only a single thermal sensor located near the CPU. Since the CPU is a large heat source, and one whose power consumption is highly subject to the computational task involved, this approach has been prudent. Still, thermal sensors have a number of limitations which make their use sub-optimal. One limitation is that thermal sensors are generally physically separated from the circuits they monitor. (This is true even if the thermal sensor is part of the CPU die.) Thus, the temperature indicated by a thermal sensor is only a rough estimate of the temperature of a device. Another limitation is that thermal sensors rely on the transfer of thermal energy from the circuits generating heat. This takes time. Thus, the current temperature indicated by a thermal sensor most accurately reflects the temperature of a device at some prior time. Yet another limitation is that thermal sensors located near a CPU are dominated by CPU thermal events. Thus, even though other system components may generate a significant amount of heat (representing a significant amount of power consumption), this generally goes undetected.
Inactivity timers, on the other hand, are generally used to power down input-output (I/O) ports and peripheral devices when they have not been used for a specified amount of time. As such, inactivity timers generally do not protect devices from an over temperature condition when they are being used.
Thus, it would be beneficial to provide a mechanism to protect electronic circuits from an over temperature condition based on a direct measure of a circuit's power consumption.